This invention relates generally to a method of securing a loose pipe liner within a rigid conduit typically formed of metal such as mild steel. This invention also relates generally to a method of flaring a loose pipe liner extending from and secured within a rigid conduit.
It is known to line rigid metallic pipe with materials such as rubber, glass, and polymeric materials.
Generally, resilient pipe liners are used to form a corrosion barrier between a rigid metal conduit and a corrosive material carried through the pipe. Lined pipe is also frequently used where it is essential to maintain the purity of process streams, such as in the processing of food products or in generating stations where contamination of deionized water with iron and other metallic ions must be avoided. Also, lined pipe is used where sudden pipe failure due to corrosive action or physical impact would cause personal injury.
Resilient pipe liner is generally made from thermoplastic materials. These materials are rigid at room temperature but become pliable at elevated temperatures. Polymeric thermoplastics in present general use as lining materials for rigid metallic piping systems include polyvinylidene fluoride, polyvinylidene chloride, polypropylene, polyethylene, polytetrafluoroethylene and the like. In addition to the above noted plastic liners, liners made from materials such as rubber are capable of being flared through the instant method.
A polymeric lined pipe system is customarily assembled from individual pipe sections and fittings by bolted flanges at joints of pipe sections and fittings. As used herein, the term "pipe joint", or "joint" will be understood to include flange connections of pipe sections, also often called "spools", flange connections of a pipe fitting such as an elbow or tee with other pipe fittings, and flange fittings for joining with equipment such as pumps and vessels. A surface having a mating flange such as a tank or pump connection may not ordinarily be understood as a flange connection. Nonetheless a surface to which a flange can be secured such as a vessel having a flange connector is here considered a part of a flange fitting. Each pipe joint necessarily involves two pipe sections. It is further understood that a single pipe section may form a part of more than one joint: one joint as in the case of a blind end fitting, two joints as in the case of a linear pipe section, three joints as in the case of a tee or wye fitting.
A complete flange joint, or connection, of pipe sections necessarily comprises two fitting flanges joined by compressing together the faces of the flanges with fasteners, generally threaded bolts, or studs. For pipe lined with a corrosion resistive polymeric liner, the polymeric liner is flared, or molded, radially to extend over the metallic flange face. The polymeric liner is thus formed to a polymeric annular flange. Two or more sections of lined pipe may be joined to form a unitary lined pipe system. A sealing interface is formed by compressing the opposing annular flanges of the flared polymeric liner of each opposing pipe joint section by fasteners joining the metallic flanges in the customary manner of unlined pipe connections. Also, a section of lined pipe may be connected to an unlined pipe section. In the case of a connection of a lined pipe section to an unlined pipe section, the flared polymeric liner of the lined pipe joint section may be compressed to form a sealing interface by an opposing flange of an unlined pipe section. Alternatively, a separate gasket of an elastomeric material may be added to the joint between the flared liner faces.
When dealing with lined pipe spools, the resilient pipe liner will have both ends flared. One end of pipe liner material may be flared prior to inserting the liner into a rigid pipe. The second liner end must be flared with the liner in the bore of the rigid pipe. Alternatively, both ends of the liner may be radially flared while the liner is in the bore of the rigid pipe. Flaring is accomplished after the liner end, which is rigid and unpliable at ambient temperatures, has been heated to a temperature sufficient to make the liner pliable. A heat gun can be used to heat the liner, although any device which brings the liner to a temperature where the liner is pliable will work. A torch may be used to heat the liner. Care must be exercised when using a torch to avoid overheating the thermoplastic liner so as to degrade the liner.
After adequate heating, the now pliable thermoplastic liner may be flared, or molded, radially to extend over the metallic flange face. The flared flange serves to maintain the pipe liner within the conduit by preventing the pipe liner from sliding out through either end of the rigid conduit. The flared flanges also serve to form a seal at a pipe joint. The seal formed by the flared flanges of pipe liner material of separate pipe pieces prevents escape of pipe contents, and prevents contact of pipe contents with the rigid pipe, generally steel, at the pipe joints. The flared liner flange may be trimmed to an appropriate shape after being formed, as necessary.
One method of fabricating a spool of lined pipe begins by inserting loose pipe liner having at least one unflared end into rigid metal pipe. The outer diameter of the liner should be nearly the same dimension, but somewhat smaller than the inner diameter of the rigid pipe so as to permit the liner to slideably engage the rigid pipe. The length of pipe liner to be inserted into the bore of rigid pipe is selected such that the liner extends beyond the end of the rigid conduit a distance that when radially flared, the polymeric liner will form a sufficient flange.
In order to form a flange of the polymeric liner material it is convenient to secure the liner in position relative to the rigid pipe during the mechanical operation of forming the flange of polymeric liner.
A device known in the art used to secure the pipe liner consists of an elastomeric torus compressed between two washers. The uncompressed torus is sized such that the larger circumference can slide inside the bore of the liner. The diameter of the washers approximates the larger diameter of the uncompressed torus. The torus device is used to secure the liner to the rigid pipe by inserting the device into the liner and compressing the torus between the opposing washers. The opposing washers are compressed toward one another by a bolt, or other means. As the minor circumference of the torus is compressed, the major circumference of the torus expands. The expanded major circumference then forceably contacts the liner. The resilient liner material is deflected and in turn forcefully contacts the wall of the bore of the rigid conduit so as to secure the liner within the conduit and maintain the relative position of the liner and the conduit.
The torus device suffers from several disadvantages. For example, the expanded torus and compressed washers block the bore of the liner. As a consequence of the blockage of the liner bore a heat gun used to make the liner pliable develops back pressure increasing the heat gun temperature and thus shortening its life. The application of heat necessary to render the thermoplastic liner pliable may cause the elastomeric torus to exceed the temperature at which the elastomeric torus begins to degrade. The elastomeric torus is frequently made of a rubber compound which has substantially less heat tolerance than resilient pipe liner material such as polytetrafluoroethylene, for example.
Another device known in the art which secures a liner within a rigid conduit resembles a hat expander. The expander device comprises a pair of arms each having a first end and a second end. The first ends contact the pipe liner and are conformed to an axial and circumferential segment of the liner. The second ends are threaded in opposite directions and engage with a single nut. Rotation of the nut in one direction moves both first ends further apart. Rotation of the nut in the opposite direction moves both first ends toward each other. Placed inside the liner, rotation of the nut to separate the first ends forceably engages the liner with the rigid pipe. A disadvantage of this device is that the nut becomes more difficult to turn as the diameter of the pipe liner reduces, and as the distance from the open end of the liner to the expander increases, since the space needed to apply a wrench, or other similar instrument, diminishes.
The skilled artisan will recognize that these problems and others are solved by the present invention which has as an object to provide an improved method of securing the liner within a rigid conduit.
A further object of this invention is to provide a method of conveniently expanding a liner mandrel.
A further object of this invention is to provide a method of securing the relative position of a resilient liner material within a rigid pipe while fashioning a flange from the liner material.
A further object of this invention is to provide a method which would allow lined pipe sections to be fabricated at the construction site as the need arises. Such a method would secure loose pipe liner inside the metal pipe.
Another object of this invention is to facilitate flaring loose pipe liner within a rigid conduit.